In recent years, manufacturers have relied upon several processing techniques to manufacture sputter targets from aluminum alloys such as, aluminum-copper aluminum-silicon and aluminum-silicon-copper alloys. Manufacturers have traditionally relied upon a combination of cold working and annealing to produce a fine-grained aluminum alloy target. The annealing recrystallizes the grains to produce a useful grain texture for sputtering. The final grain size of these annealed targets typically ranges from 30 to 75 xcexcm. Reducing a target""s grain size from these levels could further improve sputter uniformity.
Target manufacturers have relied upon equal channel angular extrusion (ECAE) to produce fine aluminum-alloy microstructures. Nakashima et al., xe2x80x9cInfluence of Channel Angle on the Development of Ultrafine Grains in Equal-Channel Angular Pressing,xe2x80x9d Acta. Mater., Vol. 46, (1998), pp. 1589-1599 and R. Z. Valiev et al. and xe2x80x9cStructure and Mechanical Behavior of Ultrafine-Grained Metals and Alloys Subjected to Intense Plastic Deformation,xe2x80x9d Phys. Metal. Metallog., Vol. 85, (1998), pp. 367-377 provide examples of using ECAE to reduce grain size. ECAE introduces an enormous strain into a metal without imparting significant changes in workpiece shape. Although this process is effective for reducing grain size, it does not appear to align grains in a manner that facilitates uniform sputtering or provide an acceptable yield-the low yield originates from the ECAE process operating only with rectangular-shaped plate and thus, requiring an inefficient step of cutting circular targets from the rectangular plate.
Another mechanical method to produce fine grain structures in metals is xe2x80x9caccumulative roll bondingxe2x80x9d where aluminum sheets are repeatedly stacked and rolled to impart sufficient strain required for ultra-fine grain sizes. N. Tsuji et al., xe2x80x9cUltra-Fine Grained Bulk Steel Produced by Accumulative Roll Bonding (ARB) Process,xe2x80x9d Scripta. Mater., Vol. 40, (1999), pp. 795-800. The repeated stacking and rolling allows rolling to continue after the metal reaches a critical thickness. Although this process is useful for producing some products, the method often introduces undesirable oxides into the finished product.
Researchers have explored using cryogenic working to increase the forming limits of aluminum alloy sheet panels. For example, Selines et al. disclose a cryogenic process for deforming aluminum sheet in U.S. Pat. No. 4,159,217. This cryogenic process increases elongation and formability at xe2x88x92196xc2x0 C. In addition, similar work has focussed on increasing the formability of sheet panels for automotive applications. Key references include: i) H. Asao et al., xe2x80x9cInvestigation of Cryogenic Working. I. Deformation Behaviour and Mechanism of Face-Centered Cubic Metals and Alloys at Cryogenic Temperature,xe2x80x9d J. Jpn. Soc. Technol. Plast., Vol. 26, (1985), pp. 1181-1187; and ii) H. Asao et al., xe2x80x9cInvestigation of Cryogenic Working. II. Effect of Temperature Exchange on Deformation Behavior of Face-Centered Cubic Metals and Alloys,xe2x80x9d J. Jpn. Soc. Technol. Plast., Vol. 29, (1988), pp. 1105-1111.
Lo, et al., in U.S. Pat. No. 5,766,380, entitled xe2x80x9cMethod for Fabricating Randomly Oriented Aluminum Alloy Sputtering Targets with Fine Grains and Fine Precipitatesxe2x80x9d disclose a cryogenic method for fabricating aluminum alloy sputter targets. This method uses cryogenic processing with a final annealing step to recrystallize the grains into a desired texture. Similarly, Y. Liu, in U.S. Pat. No. 5,993,621 uses cryogenic working and annealing to manipulate and enhance crystallographic texture of titanium sputter targets.
The invention is an aluminum alloy sputter target having a sputter target face for sputtering the sputter target. The sputter target face has a textured-metastable grain structure. The textured-metastable grain structure has a grain orientation ratio of at least 35 percent (200) orientation. The textured-metastable grain structure is stable during sputtering of the sputter target. The textured-metastable grain structure has a grain size of less than 5 xcexcm.
The method of forming aluminum alloy sputter targets first includes the step of cooling an aluminum alloy target blank to a temperature of less than xe2x88x9250 xc2x0 C. The aluminum alloy target blank has grains of a grain size. Then deforming the cooled aluminum alloy target blank introduces plastic strain into the target blank and reduces the grain size of the grains to form a textured-metastable grain structure. Finally, finishing the aluminum alloy target blank at a low temperature sufficient to maintain the textured-metastable grain structure forms a finished sputter target.